Water in its natural state seldom has the qualities of potable water but we mi ensure that only potable water is consuming for good health some household methods (j making water safe for drinking are boiling.

This is the best method for making water pure for household purposed | Water should be boiled for a minimum of 31 minutes at 212° F. Water becomes tasteless on boiling because of the absence of dissolved air in it. To restore its taste again, water: should be poured from one container to another for a number of times.

Advantages

• It is a simple method and does not requirements any special equipment.

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• Solid substances like chalk powder, carbonic compounds and pathogenic microorganisms are destroyed by boiling.

• Temporary hardness and salinity of water is also reduced on boiling.

Disadvantages

• More fuel is consumed in boiling water.

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• The method is time consuming as it takes time to boil and cool down before it can be consumed.

• It is quite cumbersome to boil large quantity of water for the entire family.

• Boiling makes water tasteless. Therefore to make it tasty again, boiled water should poured from one container to another a number of times.

2. Filtration

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Water is purified at home by the following methods of filtration:

(а) Straining through muslin cloth.

In this method, water is strained through fine muslin cloth. But this filtered water is not free from bacteria because the muslin cloth cannot hold out bacteria, impure gases, and dissolved impurities. Keeping muslin cloth always clean is another drawback of this method.

(b) Four pitcher system

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In this method, four earthen pots are put one above another in a special stand. The top three spots have small hole at the bottom. Muslin cloth is used to plug the hole of the first pitcher for the slow filtration of the water. The second pitcher has coarsely crushed coal in it. Charcoal absorbs the undesirable smell from the water. The third pitcher has graded gravel and sand. The fine sandy layer holds back the bacteria. The water in the bottom pitcher is now safe for drinking. The drawback of this method is, that it is difficult to clean the contents of these earthen pots at home. This method is very time consuming also. But in villages this is the easiest and cheapest way to clean water.

(c) Filter

There are many filters avai­lable in the market. Some of these filters are as follows:

Tap filter

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These filters are fitted with the taps. It can remove suspended particles of the water but not the bacteria.

Domestic filter

It is made up of bone china or transfusion earth. It has porous candles in it. These candles are of two types: (i) Coarse grain candles (ii) Fine grain candles. In coarse grain candles all the impurities and bacteria are not filtered. Hence, it is essential to boil and disinfect this water. In fine grain candles, the filtered water is free from all impurities. But it is necessary to disinfect the candles by boiling them time to time.

Electric filter

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First the water is made to pass through three chambers. First chamber is porcelain candle where suspended particles are removed. Then the water passes through second chamber which has activated carbon particles to absorb the colour, odour, and free chlorine. After this water passes through

UV light which disinfects the water and makes it germ free to a large extent. This is a safe way to disinfect water but it is very expensive and cannot be used without electricity.

Use of chemicals

Certain chemical compounds like alum, chlorine, copper sul­phate, quick lime, potassium permanganate, etc. are used for the purification of water.

• Chlorine. Use of chlorine is the cheapest, simple, effective and the most reliable method to disinfect water. This is used to purify large quantity of water such as water tanks. It destroys bacteria in water but does not remove the suspended impuri­ties. Hence, water is filtered before chlorination.

Its ratio with water is 1:20 lakhs. These days chlorine tablets are available in the mar­ket in the brand names like Halasana, Chlordecho. These tablets are used only to disinfect water at home. For this one chlorine tablet is added to 10 liters of water and allowed to stand for 25-30 minutes and then filtered. These tablets can be conveniently used by travellers, military camps, etc. Tablets should be kept dry.

• Alum or Pitcairn. This is also a chemical method for the purification of wa­ter. This method removes all types of impuri­ties and bacteria from the water. In this method, alum is added to the impure water. By the reaction of alum, suspended impuri­ties settle down at the bottom after coagula­tion which can be separated by filtration. Alum has disinfecting qualities, hence, destroys all the bacteria in water but it does

not react chemically with water.

• Bleaching powder. Water can also be purified by bleaching powder. When bleaching powder is added to the water chemical reaction takes place and chlorine gas is produced. This chlorine gas purifies the water; Amount of bleaching powder to be added in water depends on the amount of impurities in water. Normally 30 Gms of bleaching powder is added to 100 gallons of water for purifying it.